The present invention relates to a variable valve timing device for controlling the opening and closing of intake or exhaust valves of an internal combustion engine.
One such conventional variable valve timing device is disclosed in Japanese Utility Model Laid-open Print No. 2-50105 which was published in 1990 without examination. This variable valve timing device includes a rotational shaft for opening and closing a valve, a rotational transmitting member rotatably mounted on the rotational shaft, a vane connected to the rotational shaft, an operating chamber defined between the rotational shaft and the rotational transmitting member and divided into an advancing angle space and a delaying angle space by the vane extended into the operating chamber, a first passage in fluid communication with the advance angle space for supplying and draining a fluid therein and therefrom, respectively, a second passage in fluid communication with the delay angle space for supplying and draining the fluid therein and therefrom, respectively, a retracting bore formed in the rotational transmitting member; a spring-biased locking pin fitted in the retracting bore, a receiving bore formed in the rotational shaft and having a bottom expected to receive the locking valve when the receiving bore is brought into alignment with the retracting bore due to in-phase relationship between the rotational shaft and the rotational transmitting member; and a third fluid passage for supplying an oil to the receiving bore, wherein the third fluid passage is in continual fluid connection to the first fluid passage.
In the conventional variable valve timing device, due to the continual fluid communication between the first fluid passage and the third fluid passage, when an oil supply to the advancing angle space from the first fluid passage is established concurrently with an oil drain from the delaying angle space into the second fluid passage, the receiving bore is supplied with the oil from the first fluid passage via the third fluid passage. Due to the resulting oil supply, the locking pin is retracted into the retracting bore, and the head portion of the locking pin disengages from the receiving bore. Thus, the locking condition between the rotational shaft and rotational transmitting member that was established by the locking pin is released with the result that the rotational shaft rotates in an advancing angle direction relative to the rotational transmitting member.
If an oil supply to the delaying angle space from the second fluid passage and an oil drain from the advancing angle space into the first fluid passage are established concurrently, contrary to the above, the rotational shaft rotates toward a delaying angle position relative to the rotational transmitting member. In addition, an oil drain is established from the receiving bore into the third and the first fluid passages which results in no oil pressure being applied to the spring-biased locking pin and the locking pin being brought into engagement with the receiving bore when the inner rotor and the outer rotor are in-phase with each other, such that the rotational of the inner rotor relative to the outer rotor is prevented.
However, in the foregoing or conventional variable valve timing device, whenever the device is in operation, the locking pin is brought into engagement with or disengagement from the receiving bore. In light of such repetitive locking and unlocking movement of the locking pin, to prevent damage to the locking pin, the locking pin has to be made of a relatively high cost material.
In addition, as a result of the continual fluid communication between the first fluid passage and the third fluid passage, a relatively complex fluid pressure control system is required for retracting the locking pin from the receiving bore that is capable of positioning the receiving bore to receive therein the locking pin intermediately between the most advancing angle position and the most delaying angle position.